Thanos,C. A. and Skordilis, A. (1987), Seed Sci. & Techno/.. IS, 163-174

The effects of light, temperature and osmotic stress on thegermination of Pinus halepensis and P. brutia seeds

c. A. THANOS and A. SKORDILIS

Institute of General Botany, University of Athens, Athens 15701, Greece

(Accepted May 1986)

Summary

Seeds of the mediterranean pines, Pinus halepensis and P. brutia. genninate optimally at 20°C in darkness.Their temperature range of gennination is rather narrow and their rate very slow. When seeds are osmoti-cally stressed the rate becomes even slower, while final gennination percentage is inhibited only at verylow osmotic potentials. Continuous red light or diurnal white light always promote gennination rate andsometimes maximum percentage, as well. Intermittent far-red light not only inhibits gennination in bothspecies, but also induces a secondary donnancy, shown to be under phytochrome control. Experimentsunder daily alternating conditions of light and temperature resembling those which are naturally met, leadto the conclusion that field germination is feasible throughout the rainy season of the mediterranean-typeclimate and is strongly favoured in open, sunny sites.

Resume

Effets de la lumiere, de la temperature et de la pression osmotique sur la germination des semences de Pinushalepensis et P. brutia.

Des semences de pins mooiterraneens,Pinus halepensis et P. brutia, ont une gennination optimum a 20°Ca l'obscurite. Leur gamme de temperatures de gennination est assez etroite et leur vitesse de germinationtres lente. Lorsque les semences sont soumises a une pression osmotique, cette vitesse devient meme encoreplus raible, tandis que Ie pourcentage final de gennination n'est affecte qu'a potentiels osmotiques tresfaibles. Une lurniere rouge continue ou une lumiere blanche illume favorisent toujours la vitesse de germina-tion et parfois egalement Ie pourcentage ml}ximum. Une lurniere intermittente rouge-lointain, non seulementinhibe la gennination des deux especes, mais elle induit egalement une donnance secondaire, demontreeetre sous contr6le du phytochrome. Des experimentations sous des conditions quotidiennes de lumiereet de temperature alternees, comparables a celles que l'on rencontre naturellement, conduisent a la conclu-sion que la germination en champ est possible tout au long de la saison pluvieuse dans les climats de typemediterraneen et qu'elle est fortement favorisee dans les sites ouverts et ensoleilles.

Zusammenfassung

Der Einflufi van Licht, Temperatur und osmotischem Strefi auf die Keimung der Samen van Pinus halepensisundP. brutia.

Samen der mediterranen Kiefern Pinus halepensis und P. brutia keimen optimal bei 20°C im Dunkeln.Ihr Keimtemperaturbereich ist ziemlich eng und ihre Keimgeschwindigkeit sehr langsam. Wenn Samenosmotisch gestreBt werden, wird die Geschwindigkeit noch langsamer, wobei der erreichbare Prozentsatzder Keimflihigkeit schon bei geringen osmotischen Potentialen vermindert wird. Dauerrotlicht oder tiig-

163

C. A. THANOS AND A. SKORDILIS

liches WeiBlicht fordert die Keimgeschwindigkeit stets und manchmal gleicherweise auch die maximaleKeimfahigkeit. lntermittierendes Dunkelrotlicht hemmt nicht nur bei beiden Arten die Keimung, sondeminduziert auch eine sekundiire Dormanz, die nachweislich unter Phytochromkontrolle steht. Untersuchun-gen mit tiigiich wechselnden Licht - und Temperaturbedingungen, die den natiirlich gegebenen entsprechen,lassen den SchluB zu, daB ein Feldaufgang wiihrend der gesamten Regenzeit des mediterranen Klimatypsmogiich und in ofTenen, sonnigen Lagen stark begiinstigt ist.

Introduction

Pinus halepensis P. Miller (Aleppo pine) and Pinus brutia Tenore (Calabrian pine)are by far the commonest pin~ species around the Mediterranean basin. Althoughit is evident that both species are well adapted to the mediterranean-type climate thereis a clear cut separation in their natural distributions. P. brutia is found in the relativelysmaller NE corner while P. halepensis grows allover the rest of the mediterraneanregion as well as on the Moroccan Atlantic coast. The natura:l distribution of P. hale-pensis in Greece is restricted to the large part of the mainland and the neighbouringislands. On the other hand, P. brutia grows in the north-eastern part of the mainland,the islands of the east Aegean sea and Crete (Panetsos, 1981).

The climatic pressure exerted on the plants growing in regions with a mediterranean-type climate (especially the drought stress) is accompanied by a gradually increasinghuman impact expressed either directly (e.g. land management) or indirectly (e.g. fires,overgrazing). Therefore, the investigation of the adaptive mechanisms concerning seedgermination and seedling establishment and survival are of great importance to bothconservation and regeneration, natural or artificial, of the mediterranean pine ecosys-tems.

Experimental data about P. halepensis and P. brutia seed germination are scarce.Nevertheless the effect of light operating via the phytochrome system on the promotionof seed germination, especially after prechilling, in some American pine species aswell as in P. sylvestris is well documented (Toole, 1973).

The ISTA Rules (ISTA, 1976) prescribe for the seed germination ofF. halepensis:20 °C and white fluorescent light for at least eight hours per day. Recent works onP. brutia by Shafiq (1979) and Calamassi (1982), have shown that there is also a signifi-cant promotive effect of light on seed germination. Thalouarn (1975, 1976) reporteda dramatic increase in the germination rate of P. halepensis seeds by the successiveadministration of mercuric and chloric ions. This effect can be attributed to the physi-cal and chemical properties of the seed coat. Thus, the seed coat could be consideredresponsible for the significant delay of germination. Falusi, Calamassi and Tocci(1983) studied the water potential effects on seed germination and root growth ofP. halepensis from different districts and found that their behaviour under stress wasvery different.

In the present work the effect of various factors on seed germination of P. halepensisand P. brutia are examined. These factors comprise temperature (constant or alternat-ing), light (white or chromatic) and water (osmotic) stress.

164

GERMINA TION OF PINUS SEED

Materials and methods

Seeds of P. halepensis andP. brutiawere obtained from the Forestry Division, Ministryof Agriculture, Greece. They had been collected from Istiaia and Thasos respectively(1983 harvest). Throughout the experimentation period, seeds were stored at roomtemperature (20 :t 5 °C) in darkness. At the beginning, seeds were dusted with fungi-cide (Thiram). Its use, though obviously not inhibitory to germination, was necessaryfor the prevention of fungal infection, especially at high temperatures. Before the ger-mination tests, only damaged and insect-infested seeds were discarded but not theempty ones, since no floating method had been applied. The mean weights of P. hale-pensis and P. brutia seeds of the lots used in this work were 0.0220 :t 0.0004 g and0.0601 :t 0.0010 g respectively (n = 200).

Germination tests were performed with 25 seeds per petri dish (diameter 9 cm),each lined with two layers of filter paper, moistened with 5 ml of either deionisedwater or osmotic solution. Osmotica were mannitol (Merck) solutions and their 'liswas estimated by the van 't Hoff equation. Experiments were carried out in tempera-ture controlled chambers (Heraeus BK 5060 EL.W. Germany), where in all cases thetemperature was kept constant within :t 1°C. The chambers were equipped with whitelight and broad band red (R) and far-red (FR) light sources. The broad band oneshave already been described elsewhere (Georghiou and Thanos, 1983). The white lightsource consisted of seven fluorescent (Philips TLD 18W /33) and four incandescent(Philips Philinea 6276 x 60W) tubes. The emission spectrum was quite similar to natu-ral daylight and the total fluence rate was 15 W.m-2.

The criterion of germination was visible radicle protrusion. Measurements weretaken either once or twice a week as indicated and germinated seeds were removed.The measurements ended when no additional seeds germinated and the final experi-mental values shown in figures represent maximal germination percentages. Germina-tion values are means of six replicates. V erticallines and :t values represent standarderror.

Results

The time course of dark germination of P. halepensis seeds as a function of temperatureis shown in figure 1. It is clear that at 20 °C, germination is optimal with respect toboth rate and final percentage of germination. At 15 °C there is a slight decrease inrate and final percentage compared with 20°C, while at 25°C a significant inhibitionof germination is observed.

Corresponding results of P. brutia seed germination are presented in figure 2. Simi-larly to P. halepensis, germination is again optimal (though at lower rate) at 20°C.At 15 °C or 25 °C though, P. brutia germination is dramatically decreased, and especial-lyat 15°C where it is almost fully inhibited.

Figure 3 shows the germinability of P. halepensis seeds (counted every week) asa function of an external osmotic stress, at 15 °C in darkness. As expected, the lower

165

C. A

. TH

AN

OS

A

ND

A

. S

KO

RD

ILIS

.S~,2~

~ =

'§ .

""--+

-- ..

... ~

:!:

\\-ou

- a!

0 --

. ",II")

~oK

'~

~.

~ ~

. ~

,--.

~~"""""'~

"""""'" -+

-. ~

~

.!-~

- ~

U

~

00.

'- NE

0

-.::,

! ~

-"~;:

~~

,\

u 0

. ..

II")e -~

~...;

.,;'"..

.....

]~

...

J ,

I '"

, "

I.I

~~

=

=

=

=

=

=

~

.. N

('If,) U

O!..U

!WJ.~

I' .

. ,

, ,

. 'I

\... o,s

- ~

I ~

~-I

]~

~:~

' , -

0

\- ""'"

' ~

:1

'" -

~'"

~

'

--"e..:;., ~

~~

:::::: .

.~ .

E;0'-'

"u.-

-c 0

... I-

~~

~'--0 0

=

~~

=

.8'-'..~eo.- N

=

E ::,

I ,

, I'

, .

~

':! M

.=

e

=

=

=

..'-'=

~

..

N

"'u~o

(%)

UO

!..U!W

J.~

~

~

166

'ii*1,c#":",!,",'!

GE

RM

INA

T

ION

OF

P

INU

S

SE

ED

I I

I I

I I

I I

,...-,:e-

~~

,

... -

... -

.

T--\

fJ: '-

I r-

:!

ea."

\ I

'7 ~

",'lj

a§

T

Go

= ~

0

.~

c;o E

'S

~

.~

~

. =

S

-

tijt.s

'" '"

...

0 S

O

S:

... ,-9j

'-"/

0- 0'"

].5 ]~

... =

...

~,

=0

~";)

~

B

.- ...

;>~

--

. -

.~

0 .~

, ,

, '"

I .

I &

.0 Q

,U0

0 0

0 .-

8-~

-

... c-.I

0 .~

.o

s.~

'"

... ...

"

0 .-

0 "(

%)

uol.eU!W

Ja~

S'-

oS

v,.

'" '"

Io~

0-

" tij

" '"

oS~

oS

"I

I II

I I

I II

'-b '-~

0... 0

u-"""'

='-'

~

t.s0

- 0

'" '"

~r-

.

~:~

:~":"'~

: :::::=~

:;:::::::::::::~7

/ .

17-

-; ]

1 ]

]

... D

o t.sr--

t.s I

I "'-

~.

~

~-

t.s~

11/ ~

I;.

11 11

.. .

-- ..~

u

.~ u

.:; -

~ '"

~ ~

'.~

~

~

~

~

,\ /

Y

8/1 ~

~

§

~.§

--- ..

~

.~

~

~

// / /

/ /

I a.

~

~

.1 ~

.;

... .=

---

. 00;

:E

C:J

:=

C:J

//

0 u

.- '-.

,.- .0

~

.0 '"

.. t.s

'" t.s

'lj .

e 0

.~ ~

~

.~ ~

~

E

" t.s

~

"t.s .~

4ft C

:J ~

.~

C

:J ~

0

0 . =

~

. .-

S.-

is. v

'"

'::u", "U

o-0"

~o

-- .0

"v", 0"

I .

, .

, .",

~-r--

NoS

0 0

0 0

0 ,~

... I

,~~

=

~

- ...

c-.I '"'

t.s -

'"' '".-

(%)

UO

!.. U

! W

J.~

J 167

C, A

. TH

AN

OS

AN

D A

. SK

OR

DILIS

I I

I I

I I

I I

, ~

,If §

~~

.;3

---oa

.g .- ~

-- .

. "'":

=:e

~jb

I~

-,0

Q)

- ~

8 =

e

: '£ ~

.~

.. -=

... .

~

.§ - e

7'8./

1-:

8 ~

If}~

6'...~

~

o.

. _.-

-- .

. 0 ";

~

N/

Y1

,- ]~

,-II

~

. --

>,-

.- ~

Q

) ,0

""

Q)

;>

'"..

- ,-

~

~.-

.;0."-

. C

0

U

1j 0

.. Q

, Q

) -

';3Q

, ~

cII

.. u

'" "0

.~

';3 Q

) ~

"0

/81

0 0

... .-

cII

- Q

. 8'"

"""

-- ---

.~

'"

I "0 .=

Ici

0- ~

~

'.~

Q)

gJ '"

~

.. ~

e; .~

"0

0 ...=

~

~E

o~

... cII

~'"

""'~.,

0'" '

/I

0 ';3

~

Q.,";;"

u~

"O~

~

~

=.

~.

..e I' cII .~

, I

I I

II '"

-., :=

=

=

=

=

=

cII ,-=

- oa

.. N

"'~

~

~~

- O

J,,,,(

%)

uolJeul W

J8n ~

5 ~

...,,

. "

4) 0

'=

'I:

'=

""! ""!

""! 0;

~

""! ~

r-: ~

O~

,o.-

- N

-

\0 -

- '"

- "'.-

- '=

cII

Q., ~

2 +

I +

1 +

I +

I +

I +

I +

1 +

I .~

~

... g

---"'" '"

0 0

NO

r- =

r-

2~

°C'

~~

~

.o "".,.;

"" N

16

"" ""'.g

~~

"" -

V

\0 ,,'

cII ~

,0

~

~

cII =

0 ... .-

~

'".-

0 ~

I:

~

>,1:

oS~

.:;

- Q

) - -

.- .- ~

v v

§ ~

'0;

-: "1

f'! "1

"1 0;

"': ]u;~

.;~

~

N

\0

'" '"

'" N

V

'"

cII", cli-

O;

~

+1

+I

+1

+1

+I

+I

+I

+1

.~] e

] ~~

~

\0

0 <

::>

r- \0

'" <

::>

\0 !j...B

0...

Ii: ~

""

N

16 16

"" ~

~

.:; '" ~

';3 g -g

- '"

N

~

- ~

-

v '""

0 00;

"1 f'!

- .,;.S

~

16 ---

N

- ~

U

o Q

)gJ

+I

+1

~o~

3=

0 '"

bI) N

'OJ

bI).~.

. .-

- =

.-:=

~

~

~

~.-

~

=

~-

N

N

VI

N

...: >

-+

1 +

I .

~

~$

--=

IIE

~...

~

~~

O~

I&.

~.=

~

-~I168

GE

RM

INA

TIO

N

OF

PIN

US

S

EE

D

I' I

, "

, 0

f I

~

=

I'"';

I~

"'- .

~

~--.:::::::::::::::::~

~

~

i i

"".

~

~I

u u

~

....

"'='

Q)

s §

"'='

"'='

; ;

I ,I

" I

1 ,

. ,

':if; ";;'

0 0

0 0

0 ,2,

°~

C

D

S

.c

;.., S

(%)

UO

!J.U!

WJ80

'" ~

] "3

I O

J 1

I ,

I I

, 0

'"U

0

'-' -

U'"

'-'

'" '"

Q)

'"

=

Q)

~

]oS

...

"'='

oS=

"'=

',-

=

=

,-0,-

=-

0-

~

'.,..

'8 ~

~

t ,-

II b/J

@

II "3'""

~'""

!, 1A

0. "'=

'0.,~

. ~

.""-'

'-'II

~

U

,~

UE

~o

- 0

~o

~o

.- ~

N

-CO

N

to. ~

"'='

.",=,

~;

~;

, 0---

OD

D~

. 1A

.S

' s.

0'-' 0'-'

uU

Uu

0 Q

) 0

Q)1r)

Sir)

§ - .- -L-

,..-..O

S

oSI

I ,

I ,

I "

I r..: ";;'

00 ";;'0

0 0

0 eo

eoC

D

...", ~

.c ~

.c

(%)

UO

!JeU!W

J80 ~

~

~ ~

169

C. A. THANOS AND A. SKORDILIS

I . . , . I

6 r+-~~~ /.~ 40 r...cE~

.. 2~ /f/

0 .- . . .,; i . . I

0 1 2 3 4;, Time (weeks)

Figure 9. Time course of germination in P. halepensis seeds, imbibed at daily alternating temperatures:14 hours 20 °CjlO hours l5°C(O ,8); 10hours 15 °Cj 14 hours 10°C(O, 8). Open symbols represent samplesilluminated with continuous white light throughout the 'warm' period; closed symbols are dark controls.

the 'Ps, the slower the manifestation of germination. It is interesting to note that thereis a significant increase until the third week for osmotica higher than -0.97 MPa,while for lower ones a remarkable rise in germination is observed later on. Thus, fora mannitol solution of 0.6 M (-1.46 MPa), final germination is about 50% (morethan 70% of the water control). Similar, though faster, germination is observed at20°C (figure 4). The 2nd-week-curve closely resembles the 3rd-week one at 15°C. Theremarkably delayed rise in germination can be noticed again at low osmotic potentials,though at -1.95 MPa, germination after five weeks is restricted to only about 10%.From the data of figures 3 and 4 it is evident that the germination potential (i.e. theabsolute value of the osmotic potential required for inhibition of germination in 50%of seed population) in P. halepensis seeds has a value between 1.46 and 1.95 MPa,at both 15°C and 20°C.

Figure 5 contains corresponding data for P. brutia at 20°C. The curves presentedare quite similar (though delayed by about one week) compared with those of P. hale-pensis (figure 4). In this case too the germination potential is higher than 1.46 MPa.

The effect of intermittent broad band far-red irradiation (iFR) on P. halepensisand P. brutia seed germination is presented in figure 6. It is clear, that a long (3-week)iFR illumination applied immediately after onset of sowing, not only fully inhibitsgermination, but also induces a secondary dormancy in both species. This dormancy

170

GERMINA TION OF PINUS SEED

I , , , I

100

-+---180

-'"- 60

c0

..II

C

~ 40co~

20

~y--° 9 --,-+0 8=-- .-. -

I I . . . I

0 1 2 3 4

Time (weeks)

Figure 10. Time course of germination in P. brutia seeds imbibed at daily alternating temperatures: 14hours 20°C/IO hours 15°C (0, 8), 10 hours 15°C/14 hours 10°C (0, 8). Open symbols representsamples illuminated with continuous white light throughout the 'warm' period; closed symbols are darkcontrols.

is manifested by the inability of the seeds to germinate subsequently in darkness. Thisdeep secondary dormancy is only partly released by an intervening brief red (R) irradi-ation. In P. halepensis seeds, shorter exposures (nine or six days) to iFR result in alesser degree of secondary dormancy which can be fully reversed by R irradiation.On the other hand, the exposure of P. brutia seeds to iFR for only six days resultsin a secondary dormancy which, though less deep than that imposed by 3-week iFR,nevertheless cannot be totally reversed by subsequent R irradiation. BriefFR irradia-tion given immediately after the brief R one, results in a complete reversion of theR promoting effect. This is a clear proof of phytochrome mediation in the secondaryiFR -dormancy release.

171

C. A. THANOS AND A. SKORDILIS

The illumination of P. halepensis seeds with continuous red (cR) light results ina promotion of germination rate (figure 7). This promotion is rather slight at 20 °Cwhile it is considerable (about one week) at 15 DC. The final percentages of germinationare optimal in all cases presented in figure 7, though it must be noted that these experi-ments took place four months later than those of figure 1. This decrease (about 15%),observed in the final germination level, might thus be attributed to a loss of viabilityd~ring storage (though no test of viability had been performed).. The same remark holds for P. brutia seeds too, as shown in figure 8. There too,

there is a slight increase in germination rate by cR at 20 DC, while at 15 °C there isa more marked induction of germination by cR.

Figure 9 presents germination time courses of P. halepensis seeds imbibed at alter-nating temperatures. These two temperature regimes simulate those prevailing in natu-ral conditions during early winter (mid-November) and late spring (end of April),which roughly coincide with the beginning and the end respectively of the rainy seasonin the mediterranean-type climate of Greece. It is evident from figure 9 that P. hale pen-sis seed germination at both 200j15°C and 15°jlO°C is considerably promoted bythe white light illumination provided during the warmer period. It is worthwhile notingthat dark germination at 200j15°C is quite similar to that at 20°C in darkness (figure7). Moreover, germination courses under alternating light and darkness at 200j15°Cand 15°jlO°C are nearly identical to those at 20°C and 15°C in darkness respectively(figure 7).

The corresponding results of P. brutia seeds are shown in figure 10. Similar differ-ences are observed in this case as well, while the inductive effect of light at both temper-ature regimes appears considerably increased compared with that observed in P. hale-pensis seeds.

Discussion

The seeds of P. halepensis and P. brutia from the two regions used in this work, germi-nate in darkness without any prechilling treatment. Optimal percentage (ca. 80%) andgermination rate (Tso about two weeks) is observed at 20° for both species. Seedsof P. halepensis show a wider range of temperature requirements than those of P.brutia, since the former germinate almost optimally at 15°C as well. Nevertheless,it must be noted that germination in both species is restricted to a rather narrow rangeof temperatures, around 20°C. These results are in accordance with both the prescrip-tion of 1ST A Rules for P. halepensis (ISTA,1976) and the experimental data reportedpreviously for P. halepensis (Calamassi, Falusi and Tocci, 1984) and for P. brutia (Sha-fiq, 1979). The germination rate in both cases studied is noticeably low, a fact alreadyobserved in most Pinus species (ISTA, 1976). This delay might be attributed to theseed coat acting as a barrier to water penetration to embryo (Thalouarn, 1975; 1976).

The estimated values of the germination potential in osmotic stress, for both species,are extremely high (> 1.46 MPa). The manifestation of this property takes aconsidera-bly long period of time (e.g. seven weeks at 15°C for P. halepensis seeds). It must

172

,

GERMINA TION OF PINUS SEED

be noted that especially at the lower values of osmotic potential, germination rateis significantly decreased. For instance, at - 1.46 MPa, germination of P. halepensisbegins after two or four weeks depending on the temperature (20 ° or 15 °C respective-

ly). These results do not agree with recent data concerning the effect of water potentialon the germination of P. halepensis seeds collected from four different provenances(Falusi et al., 1983). Even their strongest seed lot (probably from the same regionas ours) presented an osmotic inhibition of germination at values lower than -4 bar(-0.4 MPa) while the corresponding value in our data was lower than -10 bar. Thisdisagreement may be due to a much higher resistance to water stress of the two seedlots used in the present work. The differencein water stress resistance might be attribut-ed to the effect of either an inherent factor or seed age and storage conditions onseed vigour. It seems more probable though that the experimental time (30 days) wasinsufficient for full manifestation of germination under water stress. This is supportedby the high value of mean germination time to germination, about 21 days, at -6bar and about 25 days at - 8 bar.

Light is generally considered as a promotor of Pinus spp. seed germination. In manycases there exists a primary dormancy which can be released by chilling and/or light(Toole 1973; ISTA, 1976). It has been proved that light control is exerted throughthe phytochrome system although its spectral characteristics in gymnosperms are amatter of dispute (Grill and Spruit, 1972). The promotive effect of white light in P.brutia seed germination has already been shown at constant temperature (20° or 21°Cwith light for eight or nine hours respectively; Shafiq, 1979; Calamassi, 1982). As faras P. halepensis, is concerned, data reported by Calamassi (1982) are contradictoryto the ISTA Rules (1976) prescription, since nine hours of illumination at 21°C inhibitgermination. The results presented in this work clearly show a marked promotionof germination in both seed lots caused by either continuousR light at constant tem-peratures (15° and 20°C) or diurnal white light at alternating temperatures (10 hoursat 15°C and 14 hours at 20°C).

The germination of P. halepensis and P. brutia seeds, intermittently illuminated byFR is fully inhibited. When seeds are subsequently transferred to darkness, the dura-tion of iFR pretreatment determines the extent of germinability, or in other wordsthe degree of the secondary (FR-) dormancy induced. This secondary dormancy isunder phytochrome control as shown by R/FR reversibility and is similar to that in-duced in many light inhibited seeds (e.g. Amaranthus caudatus;Kendrick and Frank-land, 1969). It must also be noted that the germination of the P. brutia seed lot usedseems to be more photosensitive in comparison with P. halepensis.

Experimental results of P. halepensis and P. brutia seed germination at alternatingtemperatures and light regimes have already been reported (Calamassi, 1982; Shafiq,1979). However, the alternations chosen are quite unnatural, e.g. eight hours 30°C/16hours 20°C or nine hours 21 °C/15 hours 15°C with light during the warm period.On the other hand, the aim of the present experimental design was the simulationof the environmental conditions prevailing at the extremes of the rainy season. Thegermination of both species can be manifested in all cases studied, though with a lower

173

.

C. A. THANOS AND A. SKORDILIS

rate and level at cooler temperatures. These data fit well with field observations ofnatural seed germination (an initial small part of the population germinating duringthe winter months, November to February, and a 'burst' of germination occurringin March and April). Moreover, the promotive effect of light during the 'day' is clearlyshown in the present work. This fact verifies the photophilous nature of these twospecies, a nature which allows their germination and establishment mainly in open,well-illuminated places.

Acknowledgement

This work was supported in part by a research grant (to C.A.T.) from the Universityof Athens, Greece.

References

Calamassi, R. (1982). Effects of light and temperature on the germination of seed of some provenancesof Pinus halepensis Mill. and Pinus brutiaTen. (It). [talia Forestale e Montana, 37,174-187.

Calamassi, R., Falusi, M. and Tocci, A. (1984). The effects of germination temperatures and stratificationon the germination of Pinus halepensis seed. Silvae Genetica, 33, 13~-139.

Falusi, M., Calamassi, R. and Tocci, A. (1983). Sensitivity of seed germination and seedling root growthto moisture stress in four provenances of Pinus halepensis Mill. Silvae Genetica, 32, 4-9.

Gwrghiou, K. and Thanos, C. A. (1983). Phytochrome control of skotodormancy release in Grand Rapidslettuce achenes. Physiologia Plantarum, 57, 352-356.

Grill, R. and Spruit, C. J. P. (1972). Properties of phytochrome in gymnosperms. Planta (Berl.), lOS,

203-213.International Seed Testing Association (1976). International rules for seed testing. Annexes 1976. Seed

Science and Technology, 4,51-177.Kendrick, R. E. and Frankland, B. (1969). Photocontrol of germination in Amaranthus caudatus. Planta

(Berl.) , 85, 326-339.Panetsos, C. P. (1981). Monograph of Pinus halepensis Mill. and P-inus brutia Ten., Annales Forestales,

9/2,39-77.Shafiq, Y. (1979). Some effects of light and temperature on the germination of Pinus brutia, Nothofagus

obliqua and Nothofagus procera seeds. Seed Science and Technology, 7, 189-193.Thalouarn, P. (1975). Stimulation de la genriination de Pinus.halepensis Mill. par adininistration successive

d'ions mercure et chlore. Comptes Rendus de /'Academie des Sciences, Paris, serie D, 280, 275-278.Thalouarn, P. (1976). Stimulation de la germination de Pinus halepensis Mill. par administration successive

d'ions mercure et chlore; recherche des mecanismes en cause. Comptes Rendus de /'Academie des Sciences,

Paris, serie D, 282,1857-1860.Toole, V. K. (1973). Effects of light, temperature and their interactions on the germination of seeds. Seed

Science and Technology, 1, 339-396.

174